An example of power supply apparatuses to which a selected one of different AC voltages can be supplied is disclosed in Japanese Patent No. 2,558,575. A selected one of commercial AC voltages, i.e. 400 V and 200 V, is adapted to be coupled to the power supply apparatus. The power supply apparatus includes a rectifying circuit for rectifying the AC voltage supplied to it, and two inverters. When an AC voltage of 400 V is applied to the power supply apparatus, the two inverters are connected in series in the output of the rectifying circuit, and, when an AC voltage of 200 V is applied to the power supply apparatus, the two inverters are connected in parallel in the output of the rectifying circuit. The switching between the series connection and parallel connection of the two inverters is done by the use of a plurality of switches. The switches are controlled by a switching control circuit. The switching control circuit places the switches in such a state as to connect the two inverters in series before either AC voltage is applied to the power supply apparatus, and, when either one of the AC voltages is applied, detects the AC voltage and compares it with a reference value to judge whether the applied AC voltage is 400 V or 200 V. If the applied AC voltage is judged to be 400 V, the state of the switches is maintained, whereas, if the applied AC voltage is 200 V, the switching control circuit switches appropriate one or more switches to make the two inverters connected in parallel. Further, the switching control circuit latches the result of the judgment in a latch circuit in order to use the output of the latch circuit in maintaining the two inverters connected in parallel.
The problems of this power supply apparatus include complexity of the switching control circuit, which makes the manufacturing cost high.
An object of the present invention is to provide an inexpensive power supply apparatus which can receive a selected one of a plurality of AC voltages and supplies desired power prepared from the received AC voltage.